1. Technical Field
The present disclosure generally relates to advantageous systems and methods that facilitate enhanced autogenous healing of cracks in concrete structures. The disclosed systems and methods utilize water soluble materials that may be incorporated into the concrete structure at various points in time, e.g., at the pre-hardening stage, the post-hardened stage, or combinations thereof.
2. Description of Background Art
The cost of corrosion and other structural defects in materials is devastating with respect to damage and deterioration to structures as well as the potential for human injury. From a financial perspective, the cost of corrosion alone is estimated to be over $300 billion each year in the United States. The problem of preventing corrosion and addressing other potential structural defects remains a challenge confronting the construction and maintenance industries.
Commonly, structures are made of concrete materials. Because conventional concrete has very low tensile strength, it is common practice to reinforce concrete with steel bars in applications where the concrete is subjected to substantial loads. In such implementations, the concrete has at least two functions. One function is to protect the reinforcing steel bars against corrosion. Another prominent function is to improve resistance from shear and compressive stresses. As a general matter, the protective effect of hardened concrete against climatic and environmental conditions on reinforcing steel depends, for example, on the amount and type of cement, water/cement factor and concrete integrity. However, since concrete is also a permeable absorptive material, concrete is often subject to undesirable intrusion of moisture and other substances, each of which can lead to corrosion of the reinforcing steel. Moreover, concrete structures are susceptible to cracking which provides a pathway for the invasive effects of moisture and the like.
Crack formation in concrete is a known and expected phenomenon. Various causes of concrete cracking can be observed, e.g., plastic shrinkage, plastic settlement, early thermal contraction, crazing, drying shrinkage, construction movement and/or accidental overload. In one particular example, as reinforcing steel corrodes, it expands, thus cracking (and/or further cracking) the concrete, which in turn allows for more impurity invasion, e.g., water ingress, which in turn advances corrosion as the cycle builds. Moreover, as a result of various distresses, such as environmental conditions, including at least shear and compressive stresses, accumulated after some length of service, the concrete can eventually develop structurally significant cracking which can lead to failure. In short, the noted processes have the potential for effecting premature deterioration and subsequent failure of concrete structures.
Irrespective of the cause of concrete cracking, cracks are deleterious to the generally desirable moisture barrier properties of the concrete. In concrete members where waterproof properties are desired and where cracking occurs, costly post construction repairs may be necessary to seal the cracks. In conventional concrete applications, complete hydration of Portland cement occurs over a many year span. As a result, leakage of water into cracks generally results in the water molecules contacting residual unhydrated cement. To the extent residual unhydrated cement is contacted, hydration of the cement occurs and new cementitious reaction products form in the crack area, thereby bridging the cracks and partially or fully sealing the leakage. This phenomenon has been termed autogenous self-healing of the concrete.
Efforts have been made to solve the premature deterioration of such structures. For example, U.S. Pat. No. 4,869,752 to Jaklin describes the use of modified inorganic silicates, e.g., modified alkali silicates, as a concrete additive to prevent corrosion of steel structures or reinforcing steel. U.S. Pat. No. 6,277,450 to Katoot describes the use of a coating process to coat metal surfaces which are modified to an active moiety of metal hydroxide receptive to a fully cross-linked polymer of various thickness. Other processes that have been used have included precoating surfaces of metals used in the building and construction industry. However, such methods are generally costly, ineffective and inefficient/impractical.
In commonly assigned applications, materials and systems for treatment of concrete structures have been disclosed. U.S. Patent Publication No. 2004/0237834 to Humphrey et al. discloses a composition for concrete treatment and a method for synthesis thereof. The disclosed composition is an alkali-based salt solution of a dioic acid of the following chemical formula:
wherein M+ is selected from the group comprising Na+ and K+; R1 is a C1 to C24 branch or linear aliphatic compound; and R2 is a C1 to C10 branch or linear aliphatic compound.
U.S. Patent Publication No. 2004/0237835 to Rhodes et al. discloses a further concrete treatment system that includes the alkali-based salt solution of a dioic acid of the Humphrey et al. patent publication (U.S. Patent Publication No. 2004/0237834) in combination with a defoaming agent, e.g., a polyether modified polysilixane, tri-alkane/alkene phosphates and mixtures thereof. The disclosed defoaming agent is effective in reducing excessive air entrainment and/or foaming during preparation of concrete mixes and in controlling air content of the cured concrete.
Reference is also made to a pair of publications by Mark Allyn, Jr. and Gregory C. Frantz. In a first publication, Allyn, Jr., et al. describe strength and durability testing of concrete containing salts of alkenyl-succinic acid, specifically disodium tetrapropenyl succinate (DSS) and diammonium tetrapropenyl succinate (DAS). [Allyn, Jr., et al., “Strength and Durability of Concrete Containing Salts of Alkenyl-Succinic Acid,” ACI Materials Journal, January-February 2001, pages 52-58]. In a second publication, Allyn, Jr., et al. describe corrosion testing of the foregoing materials over a 48 week period. [Allyn, Jr., et al., “Corrosion Tests with Concrete Containing Salts of Alkenyl-Substituted Succinic Acid,” ACI Materials Journal, May-June 2001, pages 224-232.] Neither of the Allyn, Jr., et al. publications provides structural details of the disclosed composition nor teachings as to synthesis of the disclosed composition.
Despite efforts to date, a need remains for treatments, materials and processes that can reduce and/or eliminate the potential for crack-related deterioration and/or failure of concrete structures. These and other needs are advantageously satisfied by the disclosed treatment systems and methods.